Electrostatic-writing system



United States Patent 3,131,256 ELEQTRGSTATHI-WRTTING SYSTEM Hugh F.Frohhach, Sunnyvale, Calif., assignor to Stanford Research Institute,Paio Alto, Calif., a corporation of California Filed May 31, 1962, Ser.No. 198,817 5 Qlairns. (til. 178-645) This invention relates toelectrostatic-writing systems and, more particularly, to an improvementtherein.

Electrostatic-writing systems of the type now known and in useconstitute an arrangement for depositing electrical charges on paper ina pattern which represents the intelligence desired to be Written.Thereafter, a toner powder is dusted onto the paper. The powder adheresonly to those areas of the paper wherein there is an electrostaticcharge. Toners dispersed in a suitable liquid may also be used.Thereafter, heat may be applied to permanently fix the powder to thepaper. Thus, the intelligence which was initially conveyed to the paperin the form of a charge pattern now appears as a visible pattern.

Various arrangements have been provided for depositing electrostaticcharges on paper in accordance with information received from signals.One system is to provide a delay line, from which many taps are takenfrom different points along the delay line. These taps are terminated aswriting styli above an insulating paper, upon which it is desired todeposit an electrostatic charge. A bar of conducting metal is located onthe side of the paper opposite to the side to which the writing styliare brought. Thus, the paper is moved between the writing styli and theback bar.

A pulse is applied to one end of the delay line. The amplitude of thepulse is such that, in and of itself, it will not cause an electrostaticdischarge from any one of the styli through the paper to the back bar.However, a signal can be applied to the back bar, having an amplitudesuch that, when it is present simultaneously with a pulse on any one ofthe styli, an electrostatic discharge will take place. By synchronizingthe application of a pulse to the delay line with the time of theapplication of a signal to the back bar and the motion of the paper, thecharge pattern can be laid down on the paper in a manner to conveyintelligence information.

One of the problems which arises with a system of this type occurs Whenit is desired to increase the number of writing styli so that thewriting density is increased. If the number of styli are increased, itis necessary to increase the number of taps made to the delay line.However, then it is necessary to insure that a pulse exists on only onetap at any instant, which requires a line which has a delay-to-rise-timeratio equal to the number of taps. At present, the maximum number oftaps avail able on lines having delay-to-rise ratios equal or greaterthan the number of taps is on the order of 100, and these are expensive.Lines having 30 to 40 taps are readily available at reasonable cost.

An object of this invention is the provision of an electrostatic-writingsystem of the type employing a tapped delay line, whereby the number ofwriting styli employed may be increased without an inordinate increasein the cost of the system.

Another object of the present invention is the provision of anelectrostatic-Writing system of the type employing a tapped delay line,wherein the number of writing styli which are driven may be increasedwithout inordinately increasing the complexity of the writing system.

Yet another object of the present invention is the provision of a noveland unique electrostatic-writing system of the type employing tappeddelay lines.

Yet another object of the present invention is the pro- 3,131,256"Patented Apr. 28, 1964 ice vision of a novel, simple, and inexpensiveelectrostaticwriting system for depositing electrostatic images ofalphanumeric characters on dielectric-coated paper incharacter-sequential fashion.

These and other objects of this invention may be achieved in anarrangement wherein there are provided a first and a second tapped delayline. A separate, elongated conductor is connected to each tap of thefirst delay line. These separate conductors are positioned to beparallel to one another and to extend in a plane along one surface of adielectric-coated paper on which it is desired to deposit electrostaticcharges. A separate, elongated conductor is connected to each tap of thesecond delay line. These are also positioned parallel to one another,and substantially in a plane, and extend at substantially right anglesto the previously mentioned elongated conductors on the side of thedielectric coated paper opposite to the side which is contacted by thefirst group: of elongated conductors. Thus, effectively, the two sets ofconductors define two opposed planes, between which the writing paper ismoved, and which two opposed planes; define the region at whichelectrostatic charge deposition occurs.

The arrangement of tapped delay lines and writing conductors may beoperated in many ways, but one which is suitable for use with videosignals enables the application of a pulse to a conductor attached to atap in one delay line, while a pulse is applied to each one of theconductors attached to the taps in the other delay line. The polaritiesand amplitudes of the pulses which are applied are such that nodischarge for depositing electrostatic charges occurs between theseconductors unless there is also present a third signal, namely, thevideo signal. Thus, a scanning action is achieved across the regiondefined by the two opposed planes, and charge deposition may take placein accordance with the information contained in the video signals.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself, both as to its organization and method of operation, as well asadditional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanyingdrawings, in which:

FIGURE 1 is a circuit, schematic diagram of one embodiment of theinvention;

FIGURE 2 is a circuit, schematic diagram of a second embodiment of theinvention; and

FIGURE 2A is a detail of a fragment of the elongated conductors ofFIGURE 2.

Reference is now made to FIGURE 1, which shows one arrangement inaccordance with this invention. There is shown a first multitapped delayline 16 and a second multitapped delay line 12. The delay-line shield10A is connected to ground. A separate, elongated conductor 14A to MN isconnected to each one of the taps on the multitapped delay line 16.These conductors are arranged to be spaced from one another, to beparallel with one another, and to be substantially in a common plane. Asshown in FIGURE 1, these conductors extend in the direction of travel ofdielectric-coated paper 16. These conductors are in contact with thesurface of the dielectric-coated paper 16.

The delay line 10 is terminated in the characteristic impedance 18 ofthe delay line It The other end, or input end, of the delay line 10 isconnected to a negative-pulse generator 20. The second multitapped delayline 12 also has a plurality of elongated conductors, respectively 22Athrough ZZF, associated therewith. A separate one of these elongatedconductors is connected to a different tap of the delay line 12A. Theseconductors 22A through 22F extend parallel to and spaced,

:3; from one another and substantially at right angles to the conductors14A through 14N. These conductors 22A through 22? are substantially in aplane and are in contact with the bottom side, or side of thedielectric-coated paper opposite to the side being contacted by theelongated conductors 12A through 14-N. Thus, effectively, the sets ofconductors 14A through 14N define one plane and the sets of conductors22A through 22F define an opposite plane, and the dielectric-coatedpaper on which electrostatic charges are to be deposited is positionedbetween these two planes and in contact with both.

The end of the delay line 12 is terminated in its characteristicimpedance 24, connected between the end of the delay line 12 and theshield 12A. A positive-pulse generator 26 applies its output to theinput end of the delay line 12 with respect to the shield 12A. Theamplitude of the output of the negative-pulse generator 2t) andpositive-pulse generator 26 is established at values such that, eventhough they are both simultaneously present at opposed elongatedconductors, no electrostatic discharge will take place unless there isan additional signal present. This additional signal is derived from thevideo amplifier 28, which amplifies video signals from a source 39,which are applied thereto. The output of the video amplifier isconnected to the delay line 12 in a manner so that the potential of theentire delay line is raised above ground by the amplitude of a videosignal. Thus, this video signal and the positive-pulse generator outputare combined and, in the presence of a negative pulse on an opposedconductor, a discharge will occur therebetween, during the interval thatall signals are simultaneously present.

The delays provided for the delay lines It) and 12 are such that ascanning action will take place. A pulse applied to the delay line willbe delayed long enough so that a pulse applied to the delay line 12' cancompletely travel therethrough. In this manner, a pulse applied to thedelay line 10 will hold the elongated conductor 14A at a negativepotential with respect to ground, while a pulse applied to the delayline 12 is applied successively to the elongated conductors 22A through22F. The pulse on delay line 10 then is applied to elongated conductor14B.

A second pulse must be applied to delay line 12, so that it may besuccessively applied to the elongated conductors connected thereto whilethe pulse applied to the elongated conductor 14B is present. Any signalsreceived from the video amplifier 28 cause an electrostatic discharge tooccur between the one of the elongated conductors 14A through 14N andthe one or more of the elongated conductors 22A through 22F, asdetermined by the interval during which a positive and negative pulseand a video signal are simultaneously present on these opposedconductors.

It will thus be seen that the delay of delay line 12' is equal to orless than the delay per tap of delay line 10, and that the output-pulserepetition rate of the positivepulse generator 26 is equal to or greaterthan the product of the output repetition rate of the negative-pulsegenerator times the number of taps on delay line 10, to which elongatedconductors are connected. After a complete scanning action has takenplace between the two planes of elongated conductors, the dielectricpaper is moved to present a fresh field for electrostatic chargedeposition between the two planes of conductors. Means may be providedto synchronize the pulses provided by the respective pulse generators 20and 26.

The system described in FIGURE 1 is operative. However, difiicultiesarise when it is desired to obtain a resolution, for example, in excessof 100 lines per inch across an 8 /2" page. This would require at least850 taps to the delay line 10. Furthermore, in order to insure that thenegative pulse exists on only one tap at any instant, it is necessary toobtain a delay line which has a delay-to-rise-time ratio equal to thenumber of taps. At present, the maximum number of taps available onlines having delay-to-rise ratios equal or greater than the number oftaps is on the order of 100, and these are expensive. Lines having 30 to40 taps are readily available at reasonable cost. One method forobtaining the equivalent of one line with 850 taps would be to use 22lines, each having 40 taps with repeating-pulse gen erators betweenthem.

FIGURE 2 presents a practical solution to the problem postulated, whichrequires far fewer delay lines and has great flexibility. In FIGURE 2there is provided a first multitapped delay line 40, a secondmultitapped delay line 42, and a third multitapped delay line 44. As inFIGURE 1, there is provided a plurality of elongated conductors, butthis time the elongated conductors are divided into groups of elongatedconductors, respectively 46A through E, 48A through E, 50A through E,and 52A through E. A diflferent one of the elongated conductors in eachgroup is connected to a dillerent tap on the delay line 40. Thus, to thefirst tap in delay line 40 there are connected elongated conductors 46A,48A, 50A, and 52A. These groups of conductors are positioned adjacentone another, substantially parallel to one another, and in a commonplane.

Delay line 42 is a multiple-tapped delay line, and a different one of aplurality of conductors, respectively 54A through 5433, is connected toa difierent one of the taps of the multitapped delay line 42. Theseelongated conductors 54A through 54E extend parallel to one another, ina common plane, and are substantially at right angles to the elongatedconductors 45A through 52E. Both sets of conductors define oppositeplanes through which the paper 56 be moved.

A third set of elongated, spaced, parallel conductors 66A through 69Gare provided. These extend substantially parallel with the conductors46A through 52E. There should be at least as many of the conductors Athrough 60G, and preferably more, than there are groups of conductors46A through 52E. These conductors 60A through 606 are notched so thatthey may be interleaved with the elongated conductors 54A through 54E.These conductors are supported therein in a manner to be insulat ed fromthe conductors 69A through 6'86 through the notches of which theconductors 54A through 54E extend. FIGURE 2A shows a section in detailof the elongated conductors 54E and 54D and the notched conductors 60Aand 6013. This is presented in order to illustrate the effectiveinterleaving of these sets of conductors. A different one of theconductors 60A through 69G is connected to a different one of the tapsalong the multitapped delay line 44 The delay line 40 is terminated atone end in its characteristic impedance 62. A negative-pulse generator64 V has its output applied across the delay line and the characteristicimpedance 62. The shield 449A of the delay line 40 is also connected tothe end of the characteristic impedance 62 connected to the negativepulse generator output.

A positive-pulse generator 66 has its output applied to one end of thedelay line 42. The other end of the delay line 42 is connected to acharacteristic impedance 63, which, in turn, is connected to ground. Theshield 42A of the delay line 42 is also connected to ground.

Another positive-pulse generator 76 has its output applied to one end ofthe delay line 44. The other end of the delay line 44 is connected toground through a characteristic impedance 72. The shield 44A of thedelay line 44 is also connected to ground.

The pulse generators, respectively 64, 66, and 70, are connected to besynchronized from a common-sync-input source. Video signals are appliedto a video amplifier 74. The output of the video amplifier is applied tothe delay line 40 in a manner to alter the potential of the entire delayline with respect to ground by the amplitude of the video signalreceived from the video amplifier.

This is achieved by connecting the output of the video amplifier to thereturn from the characteristic impedance 62, back to the negative-pulsegenerators 64.

Without the presence of the third set of interleaved conductors 60Athrough G the system shown in FIGURE 2 would behave in the same manneras that in FIGURE 1, except that when a negative pulse reached the endof delay line 40, the resulting electrostatic-charge pattern on thepaper would be repeated across the page a number of times equal to thenumber of conductor groups connected to the delay line 40. The purposeof the set of interleaved conductors 60A through G is to prevent theprinting of all groups of conductors except one. This is accomplishedsimply by putting a positive pulse on the delay line 44.

The time delays of delay lines 40 and 44 are designed so that thescanning velocities of the pulses applied to the delay line 40 and apulse supplied tothe delay line 44 are equal. That is, while pulses arebeing applied to the successive conductors in a group of conductors fromdelay line 40, pulses are also applied to those of the conductors 60Athrough 66G which are opposite this group of conductors. The time ofdelay of delay line 42 is selected so that a pulse which is applied toone of the conductors 54A through 54E will be maintained while pulsesare successively applied to all of the conductors in all of the groupsconnected to the delay line 40.

The amplitudes of the pulses received from the pulse generators areestablished in a manner so that only when a video signal is presentsimultaneously with pulses on opposed conductors can an electrostaticdischarge take place between two opposed conductors. The pulses appliedto delay lines 40, 42, and 44 insure that a scanning action take placesuccessively in lines across the paper. The video signal then caninitiate a discharge at the proper location, so that theelectrostatic-charge pattern on the paper represents an intelligiblesignal. After a complete scanning action, the paper is moved to presenta fresh surface for receiving electrostatic discharges.

The operation of the arrangement may be understood qualitatively byconsidering the field at the surface of one of the conductors 46Athrough 52E as resulting from a potential difference between the one ofthese conductors to which a pulse is applied and the small-area averagepotential directly opposite to the paper. This average potential is theaverage of the potentials of the conductors 54A through 54B and twoadjacent conductors 60A through 60G. In the absence of a positive pulseon the two adjacent conductors 60A through 606, the pulses on theconductors 54A through 54B are insufficient to raise the effectivepotential at the back of the paper high enough to cause sufficient fieldat the surface of the negatively pulsed one of the conductors 46Athrough 52E to cause field emission. Similarly, a positive pulse on oneor two of the conductors 60A through 60G will not cause a suflicientfield without a corresponding pulse on one of the conductors 54A through54E. If, however, the conductors connected to the delay line 42 and theconductors connected to the delay line 44 are positively pulsed, theiraverage potential becomes equal to the pulse height, and, together withthe negative pulse and the video signal, the field at the intersectioncan become sufficient to cause charge deposition at that point.

The net effect, therefore, is a scanning path which is geometricallyidentical to the scanning path derived from the system shown inFIGURE 1. An interesting modification may be employed, if desired, togive greater flexibility in the order of positioning of characters on aline. If, instead of using a delay line 44, an electronic selectionswitch is used, the position of a character on the line may be specifiedby the signals received from this selection switch. The ability tospecify not only which character, but where on the line it is to beprinted, may be important in some applications.

There has accordingly been described and shown here- 6 in a novel,useful, and unique arrangement of elongated conductors in order toobtain a scanning-raster pattern for electrostatic-charge-imagedeposition.

I claim:

1. An electrostatic printing system comprising a first and second delayline each having a plurality of taps spaced along the length thereof, afirst plane substantially parallel to and spaced from a second plane,said first and second planes defining an electrostatic printing regiontherebetween, a first plurality of spaced and substantially parallelelongated conductors substantially in said first plane, a secondplurality of spaced substantially parallel elongated conductorssubstantially in said second plane, said first plurality of elongatedconductors extending substantially at right angles to said secondplurality of elongated conductors, means connecting each of theconductors in said first plurality of conductors to a different one ofthe plurality of taps of said first delay line, means connecting each ofthe conductors in said second plurality of conductors to a different oneof the plurality of taps of said second delay line, and means forefiectuating electrical discharges between predetermined conductors ofsaid first and second pluralities of conductors includes a third delayline having a plurality of taps along the length thereof, a thirdplurality of elongated, spaced substantially parallel conductorspositioned behind said second plurality of elongated conductors andextending parallel to said first plurality of elongated conductors.

2. An electrostatic writing system comprising a first, second, and thirddelay line each having a plurality of taps spaced therealong, aplurality of groups of spaced, substantially parallel elongatedconductors extending substantially in a first plane, means connecting adifferent one of conductors in a different one of the groups ofconductors to a different tap on said first delay line, a firstplurality of spaced substantially parallel elongated conductorsextending in a second plane which is substantially parallel to andspaced from said first plane, said conductors in said first pluralityextending substantially at right angles to the conductors of said groupsof conductors, a second plurality of spaced substantially parallelelongated conductors, the number of conductors in said second pluralityof conductors corresponding to the number of groups of conductors, saidconductors in said second plurality being substantially coextensive andparallel to the conductors in said groups of conductors and beingnotched to afford interleaving with said first plurality of conductorswithout contact therewith, means connecting a different one of theconductors of said first plurality to a different one of the taps onsaid second delay line, means connecting a different one of theconductors of said second plurality to a different one of the taps onsaid third delay line, and means for effectuating electrical dischargesbetween predetermined ones of the conductors in said groups ofconductors and said first plurality of conductors.

3. An electrostatic writing system as recited in claim 2 wherein saidfirst delay line and third delay line have substantially the same delaytime and said second delay line has a delay equal to the delay betweenadjacent taps of said first delay line.

4. An electrostatic writing system as recited in claim 3 wherein saidmeans for efiectuating electrical discharges between predetermined onesof the conductors in said groups of conductors and said first pluralityof conductors includes a first means for generating pulses having onepolarity, second and third means for generating pulses having a polarityopposite to that of the pulses of said first means, the frequency ofpulses generated by said first and third means being substantiallyequal, the frequency of pulses generated by said second means equallingthe product of the number of conductors in a group of conductors and thefrequency of the pulses generated by said first means, means forapplying pulses from said first means to one end of said first delayline, means for applying pulses from said second means to one end ofsaid second delay line, means for applying pulses from said third meansto one end of said third delay line, means for applying intelligencesignals to both ends of said first delay line, and means for adjustingthe amplitudes of the pulses and signals to require their simultaneouspresence on an opposed conductor in a group and a conductor in saidfirst and second plurality of conductors to eifectuate an electricaldischarge therebetween.

5. In an electrostatic Writing system of the type employing a firstmultiple tapped delay line having a plurality of Writing conductorsconnected thereto and extending to one side of a dielectric medium foreffectuating electrical discharges through said dielectric medium toconductive means on the opposite side of said dielectric medium, theimprovement comprising said Writing conductors comprising a plurality ofgroups of elongated conductors spaced parallel to each other and to saiddielectric medium, means connecting a different one of the conductors ineach group to a different one of the taps of said first multiple tappeddelay line, said conductive means comprising a plurality of secondelongated conductors parallel to each other and to said dielectricmedium and oriented substantially at right angles to said firstelongated conductors, a plurality of third elongated conductors parallelto each other and to said dielectric medium and being coextensive withsaid elongated conductors in said plurality of groups of conductors,said third elongated conductors being notched to afiord interleavingwith said plurality of second conductors Without being contactedthereby, a second multiple tapped delay line, means for connecting adifferent one of said second conductors to a different one of the tapsof said second multiple tapped delay line, a third multiple tapped delayline, and means for connecting a different one of the third conductorsto a different tap of said third multiple tapped delay line.

References Cited in the file of this patent UNITED STATES PATENTSGitzendanner Sept. 9, 1952 Pendleton July 2, 1963

1. AN ELECTROSTATIC PRINTING SYSTEM COMPRISING A FIRST AND SECOND DELAYLINE EACH HAVING A PLURALITY OF TAPS SPACED ALONG THE LENGTH THEREOF, AFIRST PLANE SUBSTANTIALLY PARALLEL TO AND SPACED FROM A SECOND PLANE,SAID FIRST AND SECOND PLANES DEFINING AN ELECTROSTATIC PRINTING REGIONTHEREBETWEEN, A FIRST PLURALITY OF SPACED AND SUBSTANTIALLY PARALLELELONGATED CONDUCTORS SUBSTANTIALLY IN SAID FIRST PLANE, A SECONDPLURALITY OF SPACED SUBSTANTIALLY PARALLEL ELONGATED CONDUCTORSSUBSTANTIALLY IN SAID SECOND PLANE, SAID FIRST PLURALITY OF ELONGATEDCONDUCTORS EXTENDING SUBSTANTIALLY AT RIGHT ANGLES TO SAID SECONDPLURALITY OF ELONGATED CONDUCTORS, MEANS CONNECTING EACH OF THECONDUCTORS IN SAID FIRST PLURALITY OF CONDUCTORS TO A DIFFERENT ONE OFTHE PLURALITY OF TAPS OF SAID FIRST DELAY LINE, MEANS CONNECTING EACH OFTHE CONDUCTORS IN SAID SECOND PLURALITY OF CONDUCTORS TO A DIFFERENT ONEOF THE PLURALITY OF TAPS OF SAID SECOND DELAY LINE, AND MEANS FOREFFECTUATING ELECTRICAL DISCHARGES BETWEEN PREDETERMINED CONDUCTORS OFSAID FIRST AND SECOND PLURALITIES OF CONDUCTORS INCLUDES A THIRD DELAYLINE HAVING A PLURALITY OF TAPS ALONG THE LENGTH THEREOF, A THIRDPLURALITY OF ELONGATED, SPACED SUBSTANTIALLY PARALLEL CONDUCTORSPOSITIONED BEHIND SAID SECOND PLURALITY OF ELONGATED CONDUCTORS ANDEXTENDING PARALLEL TO SAID FIRST PLURALITY OF ELONGATED CONDUCTORS.